The primary approach system used by most airports is the Instrument Landing System (ILS). ILS facilities provide an accurate and dependable means of navigating an aircraft to most runways for landing. An ILS transmits narrow horizontal beams which let flight crews know if their aircraft is left, right, or directly on course for a runway. The signal transmitted by the ILS consists of two vertical fan-shaped beam patterns that overlap at the center. Ideally, the beams are aligned with the extended centerline of the runway. The right side beam is typically referred to as the “blue” area while the left side of beam is the “yellow” area. An overlap between the two beams provides an on-track signal to aircraft. Ideally, at the point where ILS receivers on the aircraft receive blue area and yellow area beams signals of equal intensity, the aircraft is located precisely on the approach track of the runway centerline.
Due to the presence of terrain, physical obstacles, or political situations, some approaches to runways are guided by an ILS with a beam direction not aligned with the runway centerline direction. When executing such a runway approach, flight crews must follow the ILS beams to a point, but then turn the aircraft to the true runway direction for final landing.
This misalignment between the runway centerline direction and the ILS approach line direction creates difficulties when displaying information for such an approach on high resolution symbolic visual display systems, such as conformal perspective view visual displays, because published bearing numbers and ILS signals for the runway may not provide sufficient accuracy and resolution to properly display the approach line over an extended range. Additionally, flight crews must be made aware of the existence of the offset approach, and on the whereabouts of the transition point in order to deviate from the ILS approach line and turn the aircraft towards the runway direction.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for systems and methods to accurately display lateral deviation symbology in offset ILS approaches.